The invention relates to a device for sorting bulk material, in particular pellets, comprising a vibration conveyor apparatus and a feed apparatus, which feeds bulk material to the vibration conveyor apparatus, further comprising a first outlet and a second outlet, wherein the first outlet is arranged such that the bulk material conveyed over an end of the vibration conveyor apparatus falls into the first outlet, further comprising at least one detector apparatus, which is designed to examine the bulk material conveyed by the vibration conveyor apparatus for defects and a sorting apparatus, which is designed to manipulate bulk material identified as defective by the detector apparatus and conveyed over the end of the vibration conveyor apparatus in its trajectory such that the bulk material identified as defective falls into the second outlet.
Moreover, the invention relates to a method for sorting bulk material, in particular pellets, in which bulk material is fed to a vibration conveyor apparatus, wherein the bulk material is conveyed over one end of the vibration conveyor apparatus and falls into a first outlet, in which furthermore the bulk material conveyed by the vibration conveyor apparatus is examined for defects and bulk material identified as defective and conveyed over the end of the vibration conveyor apparatus is manipulated in its trajectory such that the bulk material identified as defective falls into a second outlet.
The detecting and sorting out of defective bulk material is very important. One example is plastic pellets, which serve as the raw material for an extrusion process, in which a plastic insulation is applied to a metallic conductor. Contaminants in these pellets can impact the insulating function and should thus be detected and the defective pellets should be sorted out.
It is known to process a portion of a batch of plastic pellets into a thin plastic film and to examine this plastic film for contaminants. If no contaminants are detected, the entire batch is released. Naturally, only a small part of the pellets is thereby examined so that contaminants cannot be reliably excluded.
A device and a method for sorting pellets are known from EP 1 045 734 B1, in which a 100% check takes place. The pellets are examined for contaminants by means of an optical detector apparatus while they are still located on the transport apparatus. If the pellets are not subsequently further manipulated, they fall over the end of the transport apparatus into a first container. However, if defects are detected by the optical detector apparatus, a blowout apparatus is activated, which diverts falling pellets over the end of the transport apparatus out of its trajectory so that they fall into a second container. The angle of the transport apparatus with respect to the horizontal should in that case be selected such that the variation of the pellet trajectories is as low as possible and as few good (non-defective) pellets as possible fall into the second container. A multi-sensory arrangement for the optical inspection and sorting of bulk material is also known from DE 10 2010 024 784 A1. For sorting a diamond-containing material, it is known from GB 2 067 753 A to convey it as much as possible in one layer on a rotating drum provided with suction holes by means of a vibration conveyor, excite it to fluorescence through an X-ray source and detect the fluorescence with a photomultiplier. It is also known from U.S. Pat. No. 5,246,118 A to detect by means of an optical sensor bulk material after it leaves a vibration conveyor in free fall and to sort it out, if applicable. Moreover, a chute is known from EP 1 726 372 A1, via which a granular material is conveyed. After leaving the chute, when the material moves in the vertical direction, it is detected by means of an optical sensor.
On one hand, the disadvantage of the prior art is that only contaminants on the pellet surface can be detected by means of the known detector apparatuses since the pellets are not generally transparent. The defect detection is thereby restricted. Moreover, a not insignificant variation in the trajectories of the pellets results in particular in the case of the arrangement of the transport apparatus described in EP 1 045 734 B1. Among other things, this makes an examination of the pellets more difficult while they are in free fall.